996 research outputs found
Observations of mesoscale vertical velocities around frontal zones
Vertical velocity and reflectivity data obtained with a VHF Doppler radar over a 15-day period in October and November of 1981 are analyzed. Standard radiosonde data and surface observations were used to locate two occluded fronts, two warm fronts, and a cold front that passed the radar site. These fronts are also evident in the radar reflectivity data. Most studies of the vertical circulation patterns associated with mososcale systems have used precipitation and cloud formations as tracers. Unlike other observational techniques, the VHF radar permits the continuous measurement of the three-dimensional air velocity vector in time and height from a fixed location. With the beam in a vertically pointing position, signals are scattered from turbulent variations in the refractive index with half the scale of the radar wavelength and by regions with sudden changes in the refractive index associated with horizontally stratified layers. Generally, the strongest echoes occur at the maximum in the vertical gradient of refractivity, usually at the base of a temperature inversion, such as the tropopause. VHF radars can also be used to locate atmospheric fronts, which are characterized by static stability, large horizontal temperature gradients, large vorticities, and vertical wind shears. These radars can provide the velocity field data needed to study wave motions associated with fronts and compare the actual vertical circulation to theoretical predictions
Comparison of vertical velocities analyzed by a numerical model and measured by a VHF wind profiler
The use of wind profilers for measuring vertical velocities in the troposphere and lower stratosphere is potentially of great interest for verification of forecasts, diagnosis of mesoscale circulations, and studies of wave motions. The studies of profiler vertical velocities to date have shown that the observed patterns of ascent and subsidence are reasonable when compared to the synoptic conditions. However, difficulties arise when a direct verification of the profiler vertical winds is sought. Since no other technique can measure the vertical velocities over the same height range and with the same claimed accuracy as the profilers, direct comparisons are impossible. The only alternative is to compare the measurements to analyzed vertical velocity fields. Here, researchers compare vertical measurements made with the SOUSY VHF radar over a period of 11 days at the beginning of November 1981 to the analyzed vertical velocities produced by the European Center for Medium-range Weather Forecasting (ECMWF) model for grid points near the radar site
Probing and modulating pain-induced corticomotor excitability reduction by engaging premotor cortex activity in humans
Cranks for partitions with bounded largest part
For 80 years, Dysonâs rank has been known as the partition statistic that witnesses the first two of Ramanujanâs celebrated congruences for the ordinary partition function. In this paper, we show that Dysonâs rank actually witnesses families of partition congruences modulo every prime . This comes from an in-depth study of when a âmultiplicity-based statisticâ is a crank witnessing congruences for the function p ` n, mË , which enumerates partitions of n with parts of size at most m. We also show that as the modulus increases, there is an ever-growing collection of distinct multiplicity-based cranks witnessing these same families
Comprehensive test of nuclear level density models
For the last two decades, experimental information on nuclear level densities
for about 60 different nuclei has been obtained on the basis of the Oslo
method. While each of these measurements has been typically compared to one or
a few level density models, a global study including all the measurements has
been missing. The present study provides a systematic comparison between Oslo
data and six global level density models for 42 nuclei for which -wave
resonance spacings are also available. We apply a coherent normalization
procedure to the Oslo data for each of the six different models, all being
treated on the same footing.
Our quantitative analysis shows that the constant-temperature model presents
the best global description of the Oslo data, closely followed by the
mean-field plus combinatorial model and Hartree-Fock plus statistical model.
Their accuracies are quite similar, so that it remains difficult to clearly
favour one of these models. When considering energies above the threshold where
the experimental level scheme is complete, all the six models are shown to lead
to rather similar accuracies with respect to Oslo data.
The recently proposed shape method can, in principle, improve the situation
since it provides an absolute estimate of the excitation-energy dependence of
the measured level densities. We show for the specific case of Cd that
the shape method could exclude the Hartree-Fock plus statistical model. Such an
analysis remains to be performed for the bulk of data for which the shape
method can be applied to the Oslo measurements before drawing conclusions on
the general quality of a given nuclear level density model.Comment: 11 pages, 7 figures, published in PR
Sediment distribution and transport in the shallow coastal waters along the west coast of Denmark
Until recently, studies of the regional distribution of seabed sediments off the littoral zone of the Danish North Sea coast had been concentrated on the Jutland Bank area (Fig. 1; Leth 1996, 1998). Knowledge on the sedimentary conditions and processes along the entire west coast of Jutland has, however, significantly increased as a result of 2000 km of newly acquired high-resolution seismic and side-scan sonar data, supplemented by about 100 vibrocores. These data were collected by the Geological Survey of Denmark and Greenland (GEUS) during joint projects with the Danish Coastal Authority between 1998 and 2001 (Leth et al. 1999; Larsen & Leth 2001). The coastal zone off west Jutland displays a highly dynamic environment, where sediment transport is governed by strong tidal and wave-induced currents. The net wave-generated current is south going, while the coastal current has a net direction towards the north (Knudsen et al. 2002). The direction of the net littoral drift is southward from the outlet of Limfjorden to BlĂĽvands Huk, with net erosion north of Nymindegab and aggregation to the south; the offshore part of this depositional system has recently been studied (Larsen & Leth 2001)
The visual trainer: A visual training program for the Commodore 128
A vision therapy program was devised and written using the Commodore 128 Computer. The program is designed to be used by the patient either at home or with a therapist in the office. This program consists of options to train and enhance saccades, pursuits, convergence and divergence fusion ranges, laterality/directionality, visual memory, and eye-hand coordination. With the use of prisms and lenses the vergence and accommodative systems may also be improved
Switched capacitor DC-DC converter with switch conductance modulation and Pesudo-fixed frequency control
- âŚ